The FDM-managed FTD has generally limited features compared to FMC-managed. I would expect to see features like these also in FDM in the future, but if you need that now, the FMC for managing two FTDs is about $600 global list price. If you have a VMware-host with some resources left, that is the way to go.
You can use ASDM on Firepower appliances only when they are running ASA logical devices.
Firepower Threat Defense (FTD) logical devices cannot be managed with ASDM.
Your options to manage FTD are FDM (local manager), FMC (remote manager - on premise appliance or VM - can be cloud based as well) and Cisco Defense Orchestrator (CDO, a cloud-based Cisco-hosted service).